1. Field of the Invention
This invention relates to an improved method of synthesizing certain bis-pyrazolone oxonol compounds useful as antihalation dyes in photographic products and processes.
2. Description of the Prior Art
Photographic light-sensitive elements are often provided with antihalation layers for the purpose of absorbing reflected, scattered and/or diffused light which may adversely affect the quality of the image reproduced. Generally, such layers comprise organic dyes possessing the desired spectral absorption characteristics dispersed in a suitable matrix. Among the various types of dyes that have been employed for this purpose are pyrazolone dyes.
U.S. Pat. No. 3,933,798 of Harris L. Curtis and James W. Foley discloses and claims a class of bis-pyrazolone oxonol dyes wherein each of the two pyrazolone nuclei are substituted in the 1-position with an alkylsulfonamidophenyl moiety and substituted in the 3-position with an ester group of the formula ##STR1## wherein Z is hydrogen, hydroxy or lower alkoxy and m is an integer 2 or 3. As discussed therein, these dyes may be synthesized by condensing 2 moles of the selected pyrazolone ester having an active methylene group in the pyrazolone ring and 1 mole of glutaconaldehyde dianil or malonaldehyde dianil in the presence of a condensing agent, such as triethylamine or pyridine. Also, they may be synthesized by employing ester interchange reactions to convert one dye to different dye products containing different ester groups.
Using either of these procedures in the preparation of the aforementioned dyes wherein Z of the ester group is hydroxy, it has been customary to employ a trans-esterification reaction (ester interchange reaction) to introduce the hydroxyalkyl ester into the starting pyrazolone or into the final dye product. For example, such dyes possessing a 3-carb(.beta.-hydroxy)ethoxy substituent have been synthesized by reacting an N-alkylsulfanilamide as a diazonium salt with diethylacetylsuccinate to give a 3-carbethoxy-1-(N-alkylsulfonamidophenyl)-2-pyrazolin-5-one which is converted by trans-esterification to the corresponding 3-carb(.beta.-hydroxy)ethoxy compound for reaction with glutaconaldehyde dianil or by synthesizing a bis-1,5-[3-carbethoxy-1-(N-alkylsulfonamidophenyl)-2-pyrazolin-5-one]-pent amethine oxonol dye precursor and converting it by trans-esterification to the corresponding [3-carb(.beta.-hydroxy)ethoxy-1-(N-alkylsulfonamidophenyl)-2-pyrazolin-5-o ne]-pentamethine oxonol dye.
Though these prior procedures are useful for synthesizing small amounts of the bis-hydroxyalkyl ester dyes on a laboratory scale, they do not lend themselves to the production of large quantities. Because the pyrazolone ethyl esters, i.e., the 3-carbethoxy-1-(N-alkylsulfonamidophenyl)-2-pyrazolin-5-ones are obtained as gummy semi-solids of varying purity, they are difficult to isolate and purify without considerable loss of material which results in low overall yields of dye product. If the pyrazolone ethyl esters are not isolated and purified, condensation with glutaconaldehyde dianil gives unstable bis-pyrazolone ethyl ester dye precursors for use in the subsequent trans-esterification step. Where the trans-esterification step is conducted prior to condensation with glutaconaldehyde dianil, the hydroxyethyl pyrazolone ester produced is highly impure and can be recovered only with difficulty and in poor yields.
The present invention provides an improved method of synthesizing the desired bis-pyrazolone hydroxyalkyl ester dyes in high purity and in at least twice the overall yields obtained previously, i.e., 40-45% yield versus the 15-20% yield obtained using the aforementioned procedures. This is accomplished by synthesizing the pyrazolone ethyl ester from a p-N-alkylsulfonamidophenylhydrazine and sodium diethyl oxalacetate and then hydrolyzing the pyrazolone ethyl ester in situ to give the corresponding carboxy acid which may be readily isolated and purified prior to esterification with the appropriate glycol. The hydroxyalkyl ester formed from the acid is then condensed with the selected aldehyde dianil hydrochloride to yield the bis-hydroxyalkyl ester pyrazolone oxonol dye.
It also has been discovered that the phenylhydrazine employed for reaction with the sodium diethyl oxalacetate can be synthesized in consistently high yields by nucleophilic displacement of activated fluorine. Though facile nucleophilic displacement of aromatic fluorine compounds activated by o- and p- electron-withdrawing groups was found to occur in dipolar aprotic solvents, as reported by H. Bader et al, J. Org. Chem., 31, 2319 (1966), the only nucleophiles used were primary and secondary aliphatic amines. In the subject invention, a 1-fluoro-4-N-p-alkylsulfonamidobenzene prepared from p-fluorobenzenesulfonyl chloride and the desired alkylamine is reacted with hydrazine hydrate in an aprotic solvent to yield the corresponding p-N-alkylsulfonamidophenylhydrazine.